Covalent Bonding

Covalent Bond Chemical bond formed by the sharing of a pair of electrons

Orbital Overlap Shared pairs are actually orbitals of two atoms overlapping

Why Covalent Bonds Exist Atoms share electrons when their orbitals overlap When orbitals overlap, electrons are simultaneously attracted to both nuclei

Bond Length As atoms come closer, increasing electron density results in a decrease in potential energy of system As atoms become very close, electrostatic repulsion between nuclei increases Bond distance is a compromise between increased overlap drawing them together and increased repulsion pushing them apart There is an optimal bond distance where energy is lowest

Model for Covalent Bonding Localized electron model – molecule is composed of atoms that are bound together by sharing pairs of electrons Pairs of electrons localized on one atom are called Lone Pairs Electrons found in the space between atoms are called Bonding Pairs

Lewis Structure Show covalent bonds between atoms Dots used to represent unshared pairs of electrons Dash used to show electron pair shared in a bond Cl 2 H 2

Multiple Bonds Single Bond – shares 1 pair of electrons Double Bond – shares 2 pair Triple Bond – shares 3 pair As the number of shared pairs increases, the distance between the bonded atoms decreases

Drawing the Lewis Structure Sum up all valence electrons Write symbols for atoms involved so as to show which atoms are connected Draw a single bond between each atom Complete octets on outer atoms Place leftover electrons on the central atom Use multiple bonds if central atom does not receive an octet

Draw PCl 3 HCN ClO 3 - NO +